The overall objective of this research is to define, elucidate, and control certain steps that result in functional maturation of sperm cells in the epididymis, using the rabbit as a model. Of specific interest are the contributions of the epididymis that are responsible for enabling sperm cells to undergo capacitation and fertilization of eggs. From recent work of others 5 alpha-dihydrotestosterone (5 alpha-DHT or DHT) enhances achievement of sperm maturation in the proximal corpus epidymis in organ culture. However, no specific factor(s) have yet been identified that when directly applied to immature proximal corpus sperm can bring about the physiological change to mature sperm. Our goals include improvement of methodology for assessing functional sperm maturation by applying our in vitro capacitation and in vitro fertilization procedures along with critical examination, including ultrastructural observations, of fertilizations resulting from experimental efforts. A major goal is to develop our working hypothesis that protein components of epididymal fluids under steroidal influence(s) can be identified and assigned a direct role in the physiological conversion of immature to mature status of epididymal sperm. Additionally, understanding of essential mechanism(s) is anticipated to lead us to immunological and chemical means for control of the process of sperm maturation.